The invention relates to an electromagnetic actuator for actuating a lifting valve of an internal combustion engine. The actuator has an armature that is moved in oscillation between two magnetic coils and carries an armature shank that is guided in the actuator and that acts with an end portion on the shank of the lifting valve. Reference is made by way of example to German Published, Non-Prosecuted Patent Application DE 196 11 547 A1 for the technical background.
An electromagnetic lifting-valve actuating device for an internal combustion engine, also referred to as an electromagnetic actuator, has enormous advantages because of the freedom in terms of valve control times (i.e., in terms of the respective opening and closing point of the lifting valves) but relatively high forces have to be exerted to actuate, in particular, to open the lifting valve. Thus, it is necessary for the magnet coils and armature to have a particular minimum size. However, such systems, requiring a large amount of construction space, cannot readily be accommodated in the space available in an internal combustion engine. Furthermore, such systems, which, due to their type of construction, introduce high reaction forces into the structure of the internal combustion engine while they are functioning, must be considered to be unfavorable with regard to the radiation of noise emissions.
It is accordingly an object of the invention to provide an electromagnetic actuator for actuating a lifting valve of an internal combustion engine that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and that demonstrates a measure contributing to solving the above-mentioned problem by having the armature shank be made at least in portions of a material having a specific gravity substantially lower than that of steel.
With the foregoing and other objects in view, there is provided, in accordance with the invention, an electromagnetic actuator for actuating a lifting valve of an internal combustion engine including two magnetic coils and an armature moved in oscillation between the two magnetic coils. The armature has an armature shank with an end portion. The armature shank is guided in the actuator. The end portion is connected to and acts upon the valve shank of the lifting valve. At least portions of the armature shank are of a material having a specific gravity substantially lower than that of steel.
According to the invention, the armature shank, guiding the armature in the actuator and at the same time transmitting its oscillating movement to the lifting valve of the internal combustion engine, is to be manufactured, at least in portions, from a relatively light material to keep the mass to be moved by the actuator as low as possible. The measure makes it possible for the actuator magnet coils to be dimensioned smaller than when an armature shank is used, for example, being manufactured completely from steel. Moreover, when the moved mass is lower, lower reaction forces necessarily occur in the actuator and are introduced into the internal combustion structure surrounding the actuator, so that, at the same time, noise emissions are reduced.
As examples of preferred materials that come under consideration for an armature shank of the invention, mention may be made of titanium or titanium alloys and also ceramic materials that all possess a further advantageous property, to be precise, extremely low (magnetic) relative permeability. Such a measurement variable defines the ferromagnetic property of a material, that is to say, whether or not a material is a magnetic conductor or a magnetic nonconductor.
In accordance with another feature of the invention, the armature shank can be produced completely or partially from titanium, the titanium alloy, or the ceramic.
In accordance with yet another feature of the invention, the end portion is of one of the group consisting of hardened steels, valve steel, rolling-bearing steel, tungsten carbide, SiN, Al2O3, CerMets, and nonoxidic metal ceramics.
In accordance with a further feature of the invention, the armature shank has a second end portion, an inductively operating measuring system for determining a position of the armature is disposed near the second end portion, and a portion of the second end portion is disposed at least in a region of the measuring system and is of a material having a relative permeability lower than steel.
To be precise, on an electromagnetic actuator for actuating a lifting valve of an internal combustion engine, it may be desirable, in addition, to be capable of determining the respective position of the armature moved in oscillation, for which purpose preferably contactless, in particular, inductively operating, measuring systems may be used. Such a measuring system is preferably disposed near that end portion of the armature shank that is opposite the shank of the lifting valve. Then, not to disturb the measuring system by magnetization of the armature shank in the measurement region, it is proposed, furthermore, to manufacture the armature shank, at least in the region of the inductive measuring system, from a material that (at least in terms of the magnetic field strengths occurring with respect to the invention) is essentially a magnetic nonconductor. The permeability of the material used in the armature shank region is, therefore, to be near that of, for example, air or a vacuum.
In accordance with an added feature of the invention, different portions of the armature shank may include different materials that are selected essentially with regard to the requirements relevant for these portions. The individual portions of the armature shank are shaft stubs of greater or lesser length that are lined up and, assembled together, form the armature shank.
In accordance with an additional feature of the invention, the armature shank has regions, and at least one region of the armature shank has a cross section that is reduced relative to other of the regions of the armature shank.
In accordance with yet an added feature of the invention, the reduced cross-section is a peripheral groove.
In accordance with yet a further feature of the invention, the armature shank has a central portion and the at least one region is in the central portion.
In accordance with yet an additional feature of the invention, the at least one region is of one of the group consisting of titanium, aluminum, Tixe2x80x94Al alloys, and magnesium.
In accordance with again another feature of the invention, the portion of the second end portion is non-magnetic.
In accordance with a concomitant feature of the invention, the portion is of one of the group consisting of titanium, titanium alloys, ceramics, austenitic steel, aluminum, titanium alloys, aluminum alloys, and magnesium alloys.
Other features that are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an electromagnetic actuator for actuating a lifting valve of an internal combustion engine, it is, nevertheless, not intended to be limited to the details shown because various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.